The Microsoft Simple Encrypted Arithmetic Library (Microsoft SEAL) homomorphic encryption library has been made is open source on GitHub under an MIT License for free use. The library was developed by researchers in the Cryptography Research group at Microsoft.

The library has already been adopted by Intel to implement the underlying cryptography functions in HE-Transformer, the homomorphic encryption back end to its neural network compiler nGraph. SEAL is written in standard C++ with no external dependencies, making it easy to compile in many different environments.

Homomorphic Encryption (HE) is a technique for encryption that means data can be left encrypted but still used for computations. The computations can take place without the process doing the computation needing access to a decryption key. The results of the computations are encrypted, and only the owner of the decryption key can see the results.

SEAL was first released in 2015, and was later shown in use in Microsoft's CryptoNets demonstration. This was a demonstration of how it is possible to convert learned neural networks to a version that can be applied to encrypted data, which Microsoft termed CryptoNets. The technique allows a data owner to send their data in an encrypted form to a cloud service that hosts the network. Because the data is encrypted and the cloud provider doesn't have access to the keys needed to decrypt it, the data remains confidential. However, the neural network can still be used with the encrypted data to make encrypted predictions, and also return them in encrypted form.

There's now a move to make homomorphic encryption standardized, and Microsoft along with other industry leaders including Intel, IBM and SAP, are members of the Homomorphic Encryption Standardization group.

Microsoft's move in making the SEAL library open source could be seen as a cynical move to make Microsoft's technology the standard ahead of any decision by the other group members, especially given the piece on standardization on the SEAL pages on Microsoft that says:

"Since the technology is still quite new, and the existing libraries are very diverse in their functionality and design, we believe that a clear and public standardization effort could help."

However, the official line is that Microsoft is

"looking forward to engaging with the open-source community in continuing to develop our library. If you are interested, we warmly invite you to join us on GitHub"